It is common for various liquid chemicals, including petroleum products and by-products, to be stored in large metal tanks. These tanks are typically located at or somewhat below ground level, with their lower portions in contact with the earth. Because the metal tanks have a tendency to corrode and thus leak, it is desirable to provide means for preventing such corrosion. One common corrosion-preventing means involves altering the relative electrical potential of the tank material, so that corrosion does not occur.
This can be achieved either by connecting so-called sacrificial anodes to the tank or by including the tank in an impressed-current circuit. Sacrificial anodes are made of a metal having a higher galvanic potential than the tank metal, thereby causing a flow of current into the tank metal, at the expense of the anode, which is "sacrificed" for this purpose. In contrast, impressed-current circuits require that an external source of electrical potential be provided to drive a current through the tank metal. The anode in such a circuit merely completes the circuit between the power source and the tank/cathode. In general, cathodic protection of metal objects such as tanks and pipelines is well-known.
Another desired aspect of liquid storage is the ability to detect leaks from such tanks. It is possible for a leak to occur that is too small to be detected by conventional tracking methods used to determine loss of inventory from the tank. Even such a small leak, however, can pose a significant environmental threat, particularly if it occurs in the vicinity of a groundwater recharge zone. Spills may also contaminate the soil around a tank. The recent expansion of environmental regulations has increased the economic incentive for preventing and remediating any contamination of the soil that may occur.
Once a chemical contaminant is present in the soil, the site may be remediated in any of several ways. The contaminated soil may be completely removed and either cleaned or dumped in an appropriately constructed landfill. This method is costly and also requires removal of any structures that might be supported by the soil. Alternatively, the soil may be cleaned in situ. The contaminant may be vacuumed or washed from the soil by several methods. If vacuum extraction of the contaminant is performed, it may be advantageous to raise the temperature of the soil near the contamination, in order to decrease the viscosity, and increase the vapor pressure and volatility of the contaminant, and thereby improve the flow of the contaminant into the vacuum system. Elevation of the soil temperature is also advantageous in situations where bioremediation is used, either alone or in conjunction with vacuum extraction, as the microorganisms that consume the contaminant are typically more effective at temperatures above ambient.
Thus, it is desired to provide a system of equipment that has cathodic protection, leak detection, vacuum extraction, and thermal elevation capabilities. It is further desired that said system be relatively inexpensive and simple to install. Finally, it is desired that the system be installable on existing tanks and other equipment without interrupting the operation of such tanks or other equipment. The system of the present invention provides all of these capabilities.